Sorry - i started looking at this and got distracted! So to change items on a system-wide setting, you need to look at 'opsview.defaults' (/usr/local/nagios/etc/opsview.defaults) and find the line you want to edit.

Then, copy this value into opsview.conf (this is the file where you add your custom overrides, for example) - so in your case, add:

# Default values for servicechecks
$service_check_interval=5;
$service_max_check_attempts=3;
$service_retry_interval=1;
$service_flap_detection=1; # on
To opsview.conf (/usr/local/nagios/etc/opsview.conf) and then edit them as you please.
Best,
Sam